No, the "supermoon" didn't cause the Japanese earthquake

Japan suffered a massive earthquake last night, measuring nearly magnitude 9. This is one of the largest quakes in its history, causing widespread and severe damage. Before I say anything else, I'm greatly saddened by the loss of life in Japan, and I'll be donating to disaster relief organizations to help them get in there and do what they can to give aid to those in need.

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!

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While there isn't much I can do to directly help the situation in Japan, I do hope I can help mitigate the panic and worry that can happen due to people blaming this earthquake on the so-called "supermoon" -- a date when the Moon is especially close to the Earth at the same time it's full. So let me be extremely clear:

Despite what a lot of people are saying, there is no way this earthquake was caused by the Moon.

The idea of the Moon affecting us on Earth isn't total nonsense, but it cannot be behind this earthquake, and almost certainly won't have any actual, measurable effect on us on March 19, when the full Moon is at its closest.

So, how can I be so sure?

The gravity of the situation

Here's the deal. The Moon orbits the Earth in an ellipse, so sometimes it's closer to us and sometimes farther away. At perigee (closest point) it can be as close as 354,000 km (220,000 miles). At apogee, it can be as far as 410,000 km (254,000 miles). Since the Moon orbits the Earth every month or so, it goes between these two extremes every two weeks. So if, say, it's at apogee on the first of the month, it'll be at perigee in the middle of the month, two weeks later.

The strength of gravity depends on distance, so the gravitational effects of the Moon on the Earth are strongest at perigee.

However, the Moon is nowhere near perigee right now!

The Moon was at apogee on March 6, and will be at perigee on March 19. When the earthquake in Japan hit last night, the Moon was about 400,000 km (240,000 miles) away. So not only was it not at its closest point, it was actually farther away than it usually is on average.

So again, this earthquake in Japan had nothing to do with the Moon.

Time and tide
So why would people think this is due to the Moon?

On March 19, the Moon will be at perigee --about 354,000 km away. However, on that date it will also be full, and this has an effect on tides.

You can read my detailed essay on tides on my old website. The bullet points are that the Sun has an effect on our tides here on Earth, as does the Moon. When the Sun, Earth, and Moon are near a straight line in space -- that is, at new or full Moon -- these effects are maximized. We get what are called spring tides, with extra-high high tides, and extra-low low tides.

If this happens at perigee, the effects are even stronger. The tidal force from the Moon can be as much as 50% greater! While that sounds dangerous, it's not like we'll see huge earthquakes and roaring tidal waves from this, because even at their strongest, the tidal forces are fairly weak. It does mean people in low-lying regions and who usually experience monthly spring tide floods should take extra precautions, but it won't be the epic disaster some people are breathlessly claiming.

The pseudoscience

The UK newspaper Daily Mail has a shameful article up asking if the Japan earthquake was caused by this "supermoon". While they do ask a geologist and an astronomer about it -- and they both say it's silly -- the article spends quite a bit of its space whipping up fears that the gravity of the Moon will cause volcano eruptions and earthquakes.

I'll note that the person who is making this claim, and who first called this effect a "supermoon", is an astrologer. Yeah. Let me be clear here as well: astrology doesn't work. At all.

And that sort of thinking has failed here again. Study after study has shown that big earthquakes are not caused by the Moon, super or otherwise. It would make some sort of sense to think that maybe there is a connection, since the Moon pulls on the Earth, and the majority of earthquakes are caused by tectonic plates slipping past or under each other. However, you can look at the timing of earthquakes versus the distance (and phase) of the Moon, and at best there is a weak correlation between shallow, low intensity quakes and the Moon... and certainly none with major quakes.

Think about it: if there were some connection, and it were this obvious, geologists and seismologists would be issuing warnings every perigee and every full Moon. These are people who have devoted their lives to understanding how the Earth shakes, and would be screaming their heads off if it were something as easy and obvious as the Moon. They don't because there's no connection.

A storm isn't rising

What about weather? This one is a bit tougher.

The tides from the Moon and Sun affect our oceans and large bodies of water, and they also affect the solid Earth -- the land under you rises and falls by about a meter every single day as the Earth spins under the Moon!

As it happens, the tides affect the atmosphere as well. Since air is not solid or liquid, and has no real edge, the movement of air up and down due to tides is difficult to measure. But again, we can measure the dates and times of storms and other bad weather and compare it to the Moon, and to the best of my knowledge there is no correlation at all. Remember, meteorologists, like the other scientists I mentioned before, want to save lives. If they thought the Moon had any effect, they'd be all over it!

An article on Accuweather may be at the heart of this. The author repeats the claims of the astrologer I mentioned above, who links storms to the Moon. The article says:

There were SuperMoons in 1955, 1974, 1992 and 2005. These years had their share of extreme weather and other natural events. Is the Super Moon and these natural occurrences a coincidence? Some would say yes; some would say no. I'm not here to pick sides and say I'm a believer or non-believer in subjects like this, but as a scientist I know enough to ask questions and try to find answers.

But as I said before, the gravity of the Moon is strongest at perigee, and the Moon orbits the Earth once a month. There are actually 12 - 13 perigee every single year, so saying there was wild weather in a year when the Moon happened to be at perigee when it was full is meaningless. Unless the wild weather happened on the actual date of the "supermoon" then it must be coincidence, because on other dates the Moon was farther from the Earth!

Mind you, there are tens of thousands of thunderstorms on our planet each and every day, and conditions which give rise to them can take days to build. It's hard therefore to correlate any given weather system with the Moon.

And it gets worse. Like where the Accuweather article says this:

AccuWeather Facebook fanpage member Daniel Vogler adds, "The last extreme super moon occurred was on January 10th, 2005, right around the time of the 9.0 Indonesia earthquake. That extreme super moon was a new moon. So be forewarned..."

The problem here is that this is total nonsense. The huge Indonesian earthquake was on December 26th, 2004: fully two weeks before the Moon was at perigee. In other words, that earthquake happened when the Moon was nearly at its farthest from the Earth, minimizing its effect on us.

But back to weather: it's caused by an incredibly complex interaction between the Earth's rotation, the heat input from the Sun, the way the oceans and seas absorb and radiate heat, and a million other factors. If the Moon contributes in any way, it is very, very small compared to these other massive factors.

Conclusion

We humans like to connect events in our heads, even if they have nothing to do with each other. Skeptics refer to this as "Correlation does not imply causation". In other words, just because two things happen near the same time or place doesn't mean one actually caused the other. Out of such things are superstitions born.

Or "supermoons". I cannot say that there will be no earthquakes, volcano eruptions, or major storms come March 19 when the full Moon is at perigee. It would be silly to say that, since it's entirely possible there will be, and in fact, given how common these disasters, I can practically guarantee there will be something that happens on that date! Just as there will be on March 18, and March 20, and June 17, and September 30, and and and.

But I can be fairly certain that if such events happen, they have little or nothing to do with our Moon. And the earthquake in Japan certainly had nothing to do with the Moon, since our satellite was actually closer to its farthest point in its orbit than its nearest!

I expect we'll be seeing more terrible coverage of this as March 19 approaches. I'm already seeing it on Twitter and in the mainstream media (and we know how bad they are at covering science), and getting lots of emails from people who are hearing it from friends and family.

[UPDATE: I just found out PopSci has a solid, matter-of-fact article debunking this as well. Good on them! They even coincidentally used the same Moon picture I did.]

But I'll leave you with this: if there is any good to come of these doomsday scares, it's that they remind us that the Earth is a volatile place, and we are subject to disaster, sometimes without warning. Preparing yourself is rational and the smart thing to do! If you live in an area prone to natural disasters like earthquakes, severe weather, flooding, or what-have-you, check with your local government or the Red Cross to see what you can do to be prepared. When I lived in California we had an earthquake kit in the house, for example.

The earthquake in Japan -- and other natural disasters likely to happen in the next few days, weeks, and months -- are terrible tragedies. We're not making it any better by panicking over something we know isn't real. In the long run, and even the short term, it's science that will help us learn about these events, understand them better, and save lives. Keep a level head, think rationally, and do what you can to be prepared and to help if and when the time comes.